Nadezhdinka (Morotu District)

Dykes, sheets and laccoliths of alkaline rocks are intruded into Tertiary sediments which are metamorphosed, including coals that have been turned into coke. The margins of the larger sheets and laccoliths are of basic rocks but these grade inwards into syenites, although the basic rocks are also cut by syenite veins. Among the basic rocks are varieties which have been referred to by some workers as crinanites and by others as monzonite. The crinanites, which have ophitic textures, are composed of zoned andesine-labradorite (40-60%), analcime mixed with anorthoclase (10-20%) and dark-coloured minerals including titanaugite (up to 30%), olivine (up to 20%), biotite (up to 15%) and rare kaersutite, titanomagnetite and apatite. Among the alkali syenites biotite and analcime-bearing (up to 30%) varieties occur, and nepheline syenites have also been identified. They are composed predominantly of anorthoclase and microperthite (60-90%) and besides biotite aegirine-augite, aegirine, kaersutite, hastingsite and arfvedsonite are also present. The accessory minerals include aenigmatite, Ti-Fe oxide minerals, apatite, titanite and zircon. The chemistry and optical characteristics of the minerals have been studied in detail by Yagi (1953), including early classic work on the alkali pyroxene series; he also gives a range of rock analyses.